NEW YORK--Oil futures slid Wednesday as government storage data showed growing petroleum-product stockpiles.

Light, sweet crude for September delivery settled down 70 cents, or 0.7%, to $100.27 a barrel on the New York Mercantile Exchange, the lowest settlement since July 15. Brent crude on the ICE futures exchange fell $1.21, or 1.1%, to $106.51 a barrel.

U.S. oil supplies fell by 3.7 million barrels in the week ended July 25, the U.S. Energy Information Administration said Wednesday.

Analysts and traders surveyed by The Wall Street Journal had expected a drawdown of 1.8 million barrels. But late Tuesday, the American Petroleum Institute, an industry group, said its own data for the same week showed a drop of 4.4 million barrels.

"The [EIA] number that came out this morning didn't show as big of a draw as the API," said Anthony Grisanti, president of GRZ Energy Inc. in New York.

Gasoline supplies rose by 400,000 barrels, less than the expected 800,000-barrel gain.

Front-month August reformulated gasoline blendstock, or RBOB, settled down 2.76 cents, or 1%, at $2.8433 a gallon. But the August contract expires at settlement Thursday, and traders are already focused on the more-actively traded September contract, which settled down 2.94 cents, or 1%, at $2.8158 a gallon.

"The market didn't want to see another build in gasoline stocks, but it got it," said Jim Ritterbusch, president of energy-advisory firm Ritterbusch & Associates.

Gasoline demand is typically strongest during the summer holidays, which end after Labor Day. "Refiners have already produced enough," said Donald Morton, senior vice president at Herbert J. Sims & Co. "We really don't have any concerns over gasoline."

Stocks of distillates, including heating oil and diesel fuel, grew by 800,000 barrels, below the 1-million-barrel build that was expected.

Distillate stocks are now at their highest level since Sept. 27, 2013.

August diesel settled down 1.61 cents, or 0.6%, at $2.8906 a gallon.

Refining capacity utilization fell by 0.3 percentage point to 93.5% of capacity. Analysts had expected the operating rate to fall by 0.2 percentage point in the week.

Some market watchers are already looking ahead to fall, when refiners typically shut down units for seasonal maintenance.

"Oil production growth in the U.S. is still going to be really healthy toward the end of the year and into next year," but demand will be less robust in the fall, said Ed Kevelson, head of over-the-counter energy markets at brokerage Newedge U.S.A., which is owned by Société Générale.

Still, this was the fifth weekly storage draw and puts oil supplies at the lowest level since February.

"I am certainly not going to sell crude oil at these levels," Mr. Grisanti said